Is it getting enough water?

A little fertilizer might encourage it to leaf out.

Put your finger into the ground next to the tree. Make sure it's actually getting the water that you think you're giving it.

Dry, soggy, or damp within a couple of inches of the surface. Take a trowel and dig a little hole to one side. Do you see water or bone dry soil?

I'm going on year 2 with my Meyer lemon. I feed it 1x per month as instructed and water weekly. The poor little thing initially lost all of it's leaves. Now, the only branch with flowers is broken, and the leaves are turning yellow!

I know they do well in the area, and I have very good soil. I'm at a loss!

Unfortunately i see stress blooming on my rooting efforts regularly. Usually its a sign of the last gasp... however not always. Treat it with necessary food and keep the soil moist. Once a week watering may or may not be adequate for a youngster. Base the water on the soil and weather, not the calendar. I suggest liquid food as i hate letting the youngsters feeder roots dry out and burn in fertilizer loaded soil.

Scratch the surface of the soil to help airflow/exchange to the roots.

Steve